A pulse oximeter measures the oxygen level of blood by transmitting two different wavelengths of light through a portion of a subject's body where arterial blood is flowing. Conveniently this may be a finger or earlobe. The light which is transmitted through a patient's body is detected by a photodetector which produces a current that is a function of the pulsatile blood flow. The current produced is in response to each wavelength of light that is measured from the patient's body and these measurements may be combined by well-known algorithms such a Bier-Lambert's to produce a quantification of the oxygen content of the blood.
U.S. Pat. No. 2,706,927 discloses the computation of oxygen saturation from measurements of light absorption of body tissue at two wavelengths. A series of devices and procedures have been found using this technology. Generally a required peripheral device of a pulse oximeter is a photoelectric probe. Typically, such a probe is clamped to an appendage of a patient's body, such as an ear or a finger as stated above. Such probes require at least one light source for directing light into the appendage and at least one sensor for receiving light diffused out of the appendage. One method of obtaining light of the desired frequency has been to use a light source of indeterminate wavelength range in combination with a monochromatic filter of known bandpass.
U.S. Pat. No. 4,819,752 discloses a device having means for sensing electromagnetic energy of at least two wavelengths as it passes through a portion of a patient's body and means for processing the signals so produced so as to separate out a pulsatile portion of each signal which is related to the physiological pulse, and then determine the percent saturation as a function of the relative sizes of the pulsatile and non-pulsatile components.
Non-invasive photoelectric pulse oximetry have been used for a number of years and are supplied by several manufacturers. Typically, pulse oximeters measure and display various blood flow characteristics including but not limited to blood oxygen saturation of hemoglobin in arterial blood, volume of individual blood pulsations supplying the flesh, and the rate of blood pulsation corresponding to each heartbeat of the patient. The oximeter passes light through human or animal body tissue where blood perfuses the tissue such as a finger, an ear, the nasal septum or the scalp, and photoelectrically senses the absorption of light in the tissue. The amount of light absorbed is then used to calculate the amount of blood constituent being measured. The light passed through the tissue is selected to be of one or more wavelengths that is absorbed by the blood in an amount representative of the amount constituent present in the blood.
As stated above, generally pulse oximeters require a peripheral device such as a photoelectric probe that can be clamped to an appendage of a patient's body. The photoelectric probe generally comprises a flexible circuit board mounted with a photodetector at one end and at least one light emitting diode spaced apart from the photodetector so that the circuit board can be folded to align the photodetector over the light emitting diode. One photoelectric probe comprises a printed circuit on a flexible substrate composed of a first circuit having a photodetector mounted across terminals of the first circuit and wherein an opening is provided between the terminals so that the photodetector is exposed on the side of the substrate that does not contain the printed circuit. In a like manner a second circuit is disposed on the substrate in which two parallel connected light emitting diodes are mounted across terminals of the second circuit and wherein an opening is provided between the terminals so that the diodes are exposed on the side of the substrate that does not contain the printed circuit. The probe is then folded so that the side of the substrate that does not contain the printed circuit is facing inwardly and the photodetector disposed through the opening faces the diodes exposed through the second opening. This arrangement of the probe places stress on the solder connection of the components to the printed circuit and requires exact precision for mounting of the components over the openings in the substrate.
It is an object of the present invention to provide a flexible sensor assembly for detecting optical pulses that does not require forming an opening in the substrate for the sensor components and which has a non-conductive film secured over the components and circuitry of the sensor to prevent shorting of the circuitry during use.
It is another object of the present invention to provide a flexible sensor assembly for detecting optical pulses that is easy to produce and cost effective to manufacture.
It is another object of the present invention to provide a method for producing flexible sensor assemblies for detecting optical pulses.